docs: def setdefault(self, sid, value, dtype=F64):
          """
          Works like `dict.setdefault`: if the `sid` key is missing, it fills
          it with an array and returns the associate ProbabilityCurve
  
          :param sid: site ID
          :param value: value used to fill the returned ProbabilityCurve
          :param dtype: dtype used internally (F32 or F64)
          """
          try:
              return self[sid]
          except KeyError:
              array = numpy.empty((self.shape_y, self.shape_z), dtype)
              array.fill(value)
              pc = ProbabilityCurve(array)
              self[sid] = pc
              return pc